1. Field of the Invention
The invention relates to a secondary battery. More particularly, the invention relates to a secondary battery that includes a rolled electrode body in which a positive electrode sheet and a negative electrode sheet are rolled with a separator sandwiched therebetween.
2. Description of Related Art
There are two types of secondary batteries that include a rolled electrode body; one in which the rolled electrode body is housed vertically in a case main body and one in which the rolled electrode body is housed horizontally in the case main body. In this case, the term “vertically” refers to the rolled electrode body being housed in the case main body such that a rolling axis is perpendicular to a bottom surface of the case main body that has a shape of an open cylinder with a bottom, and the term “horizontally” refers to the rolled electrode body being housed in the case main body such that the rolling axis is parallel to the bottom surface. In this specification, the battery of the type in which the rolled electrode body is housed vertically in the case main body will be referred to as a “vertical battery” to simplify the description. Also, the cylindrical main body having a shape of an open cylinder with a bottom, together with a case cover that closes off the opening of the case main body, will be referred to as a “battery case”.
With many vertical batteries, an electrode terminal of one of a positive electrode and a negative electrode is provided on the case cover, and the other electrode terminal is provided on a bottom plate of the battery case (Japanese Patent Application Publication No. 2011-054378 (JP 2011-054378 A), Japanese Patent Application Publication No. 2003-317697 (JP 2003-317697 A), and Japanese Patent Application Publication No. 2004-111308 (JP 2004-111308 A)). This is done for the following reason. One typical structure of a rolled electrode body has a positive electrode collector portion in which only the positive electrode sheet is exposed, provided on one end in the rolling direction, and has a negative electrode collector portion in which only the negative sheet is exposed, provided on the other end. When this kind of rolled electrode body is employed in a vertical battery, the electrode terminals are provided near the collector portions, i.e., one electrode terminal is provided on each of the case cover and the bottom plate, so the structure of the battery is simple.
However, when a vertical battery is employed, the electrode terminals of the positive electrode and the negative electrode are divided between the case cover and the bottom plate, which makes them difficult to use. Japanese Patent Application Publication No. 2014-167890 (JP 2014-167890 A) describes a vertical type battery in which the electrode terminals of the positive and negative electrodes are both provided on the case cover. In this secondary battery, the structure of the rolled electrode body is designed differently. In this secondary battery, a plurality of strips of conductive tape referred to as “tabs” are adhered to both the positive sheet and the negative sheet of the rolled electrode body. The tabs of the positive electrode sheet and the negative electrode sheet are both adhered so as to protrude on the case cover side of the rolled electrode body that is vertically housed in the case. The plurality of taps of the positive electrode sheet are bundled together on the cover case side of the rolled electrode body and connected to the electrode terminal of the positive electrode. Similarly, the plurality of taps of the negative electrode sheet are bundled together on the cover case side of the rolled electrode body and connected to the electrode terminal of the negative electrode. Instead of the plurality of tabs, a plurality of protruding portions that protrude in the short direction may also be provided on each of the positive electrode sheet and the negative electrode sheet that are strip-like.